Palladium-Graphite

Palladium-Graphite, C16Pd. The reagent is prepared by treatment of PdCl2 in DM K with CSK at 100°. 

HYDROGENATION CATALYSTS Car-bonylchlorobis(triphenyiphosphine)-iridium. (l,5-Cyclooctadiene)(pyridine)-(triphcnylphosphine)iridium(I) hexa-tluorophate. Palladium-Graphite. 

Palladium/graphite in combination with copper(ll) chloride and flthium chloride is a good catalytic system for the oxidative dicarbonylation of alkenes using a 20 1 ratio of CO/O2 (Eq. 16). The ratio of diester to dimethyl carbonate is sensitive to the nature of the palladium catalyst precursor (Pd/graphite or PdCl2). 

Heterogeneous catalyst are also effective for the preparation of polymers by the Heck reaction. Palladium-graphite (Pd-Gr) was used for the synthesis of polycinnamamide from N,N -(3,4-oxydiphenylene)bis(acrylamide) and bis(4-iodophenyl) ether (equation 63). No phosphine or bipyridyl ligand was necessary. The presence of tri-< -tolylphosphine actually inhibited the reaction. The molecular weight Mw increased gradually to approximately 9 x 10 over 20 hours and then remained constant (204). 

Palladium-graphite (Pd-Gr) is useful heterogeneous catalyst for many organic reactions and polycondensations. The catalytic activities of Pd-Gr for die Heck reaction, oxidation, hydrogenation, and nucleophilic... 

Characterization of Pd-Gr. Palladium-graphite (Pd-Gr) was prepared by the reaction of potassium intercalated graphite and palladium chloride (II) as described in the literature.(i6) The palladium content by weight in palladium-graphite (Pd-Gr) catalyst was determined to be 17 % which is atout the half of the... 

Fi re 1 SEM backscattered images of palladium-graphite, a) palladium coated active carbon, b). 

The Heck Reaction. In the beginning, the Heck reaction of ethyl acrylate and iodobenzene was examined in the presence of a catalytic amount of Pd-Gr. The yield of ethyl dnnamate was determined by HPLC measurements and plotted against the reaction time (Figure 2). Pd-C was also used in order to make a comparison. The activity of palladium-graphite was much higher than that of Pd-C for the Heck reaction. Both Pd-Gr and Pd-C were easily removed by filtration after the reaction because they were insoluble in the reaction mixture. 

Materials. Palladium-graphite (Pd-Gr) was prepared by the reaction of potassium intercalated graphite and palladium chloride (II) as described in the literature.(i6) The content of palladium in Pd-Gr was determined to be 17 wt% by ICP plasma emission spectroscopy. iV . V -(3,4 -Oxydiphcnylcne)bis(acrylamide) JL was prepared by the condensation of 3,4 -oxydianiline and acrylic acid cMoride. The yield was 56 % and the structure was confirmed as described in the literature.(2) Bis(4-iodophenyl) ether 2. was prepared by the reaction of diphenyl ether, iodine, and bis[ istrifluoroacetoxy)iodobenzene in carbon tetrachloride at room temperature. The precipitate was filtered, washed with methanol, and purified by recrystallization from n-hexane. TTie yield was 59 % and the structure was confirmed as described in the literature. [Yoneyama, 1989 8] Ethyl acrylate, iodobenzene, trialkylamines, 1-decene, nitrobenzene, and all solvents used for the reaction were purified by distillation. Other materials were used as received. 

An einer mit Palladium bedeckten Graphit-Kathode wird Phenylacetonitril in methano-lischer Salzsaure in einer geteilten Zelle zu 2-Phenyl-athylamin (85% d.Th.) reduziert9. 

Hinds MW (1993) Determination of gold, palladium and platinum in high purity silver by different solid sampling graphite furnace atomic absorption spectrometry methods, Spectrochim Acta 48B 435-445. 

Dabeka, R. W. and McKenzie, A. D. (1991). Graphite furnace atomic absorption spectromet-ric determination of selenium in foods after sequential wet digestion with nitric acid, dry ashing and coprecipitation with palladium. Can. J. Appl. Spectrosc. 36,123-126. 

The catalyst used throughout this study was a 1% w/w palladium on graphite powder (S.A. 10 mV ) supplied by Johnson Matthey. 2-nitroacetophenone, 3-nitroacetophenone and 4-nitroacetophenone (all Aldrich >99 %) were used without further purification. No significant impurities were detected by GC. Gases (BOG, >99.99 %) were used as received. 

X-Ray studies confirm that platinum crystallites exist on carbon supports at least down to a metal content of about 0.03% (2). On the other hand, it has been claimed that nickel crystallites do not exist in nickel/carbon catalysts (50). This requires verification, but it does draw attention to the fact that carbon is not inert toward many metals which can form carbides or intercalation compounds with graphite. In general, it is only with the noble group VIII metals that one can feel reasonably confident that a substantial amount of the metal will be retained on the carbon surface in its elemental form. Judging from Moss s (35) electron micrographs of a reduced 5% platinum charcoal catalyst, the platinum crystallites appear to be at least as finely dispersed on charcoal as on silica or alumina, or possibly more so, but both platinum and palladium (51) supported on carbon appear to be very sensitive to sintering. 

On the other hand, the inclusion of electrocatalytically active metal nanocrystals (graphite-supported palladium, platinum, and ruthenium or gold nanocrystals) allowed... 

The application of palladium and magnesium nitrate matrix modifier for graphite furnace atomic absorption spectrometry has been discussed in detail [686]. The work has shown that a mixture of palladium and magnesium... 

The palladium and magnesium nitrates modifier has a substantial equalising effect on the atomisation temperature of the nine elements investigated. The optimum atomisation temperature for all but one element (thallium) is between 1900 and 2100 °C. This means that all elements can be determined at a compromise atomisation temperature of 2100 °C with a minimum sacrifice in sensitivity. Such uniform conditions for as many elements as possible are of vital importance if simultaneous multielement furnace techniques are envisaged. Moreover, in conventional graphite furnace AAS, uniform conditions for a number of elements can greatly facilitate and simplify daily routine analysis. 

The mechanism of stabilisation of the palladium and magnesium nitrates modifier was not investigated [749]. It is known, however, that palladium nitrate decomposes via the oxide to the metal at 870 °C, which melts at 1552 °C. The appearance temperature for palladium in a graphite furnace is around 1250 °C. As most of the investigated elements are stabilised to temperatures around 1200 °C, it can be assumed that the modifier acts by imbedding the analyte into the palladium matrix, or even by forming a kind of alloy with the analyte. 

The reduction is usually made in a multi-compartment electrochemical cell, where the reference electrode is isolated from the reaction solution. The solvent can be water, alcohol or their mixture. As organic solvent A,A-dimethyl form amide or acetonitrile is used. Mercury is often used as a cathode, but graphite or low hydrogen overpotential electrically conducting catalysts (e.g. Raney nickel, platinum and palladium black on carbon rod, and Devarda copper) are also applicable. 

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